Reports usage frequency for all the existing reports on SSRS 2000

I have an already published application running several MS SQL Server 2000 Reporting Services report.
I need a way to find from either the reporting services log or the application server (IIS) logs or windows log
to know the frequency of each report being used.

Based on this info, the business needs to know which reports are being used and to what extend?
How can I acheive this?

I have already got the IIS logs and it did not give the required info.
I have looked into the Reporting Services logs but it does not provide the info either.

Any help is appreciated

I know this is an old question but in case others need it:

Inside the Microsoft SQL Server Samples folder - you may need to download this there are pre-made reports on report usage / frequency etc. URL: http://codeplex.com/SqlServerSamples
The reports are in the Execution Log Reports folder. Open the reports to see the fields being queried and customize as needed.

Note that the above link currently gets you to 2k8 samples, with an internal link to (some) 2k5 counterparts ...

Please advise if you have further questions ...

Bill